Tubular incandescent lamp device



July 19, 1960 w. F. HODGE 2,945,978

TUBULAR INCANDESCENT LAMP DEVICE Filed March 15?? 1959* Invewtov: WiLLiam 1 Hoglg e,

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United States Patent Ofiiice 2,945,978 Patented July 19, I960 TUBULAR IN CAN DESCENT LAIVH DEVICE WilliamF. Hodge, Lyndhurst, Ohio, assignor to General Electric Company, a corporation of New York Filed Mar, 19, '195 9, Ser. No. 800,424

3Claims. or. 313-7279) Myinvention relates. generally to electric incandescent lamp devices, andmore particularly to elongated 1ncandescent lampshaving a helically coiled filament extendingaxially of an enclosing] sealed tubular envelope and secured: at'its ends to.terminal membersat the respective ends of .the envelope.

Such lamps have been provided with means for sup: porting the. coiled tungsten wire filament in spaced relation from the walls of the envelope, in the form of a plurality of transverse support members spaced along the length of the filament and fixedly secured thereto and peripherally engageable with the inner wall of the envelope. The support members may, for example, take the form of wire spirals or, preferably, sheet metal wafers or discs concentrically aflixed to the filament and having a diameter slightly smaller than the internal diameter of the envelope.

Such, lamps are intended primarily for operationin a horizontal position. Although it is feasible to operate lamps of relatively short length in a vertical posit on, lamps of longer length cannot be operated 1n a vertical position for very long because of filament distortion. The Weight of the filament causes the turns in the upper part thereof to be stretched at the operating temperature of about 2400 K. or higher, resulting in buckling of the lower part of the filament. Eventually, the hot filament touches the envelope wall and causes cracking and then failure of the lamp due to air leakage. In quartz heat lamps of this type having a length of about 10 inches, this takes a relatively long time, and lamp life may be about two or three thousand hours; however, this is considerably below the normal design life of about 5000 hours or more for such lamps. In lamps of about 25 inch length, however, the life may be reduced to as little as 100 to 200 hours.

It is therefore the principal object of this invention to provide a simple, inexpensive and effective means for preventing such distortion of the filament when the lamp is operated in a vertical position. It is a further object to provide a simple but effective means of supporting the filament at intervals along its length so that it cannot stretch sufiiciently to buckle.

In accordance with my invention, the prior art transverse support members are retained and, after assembly of the filament and its supports Within the vitreous envelope, the envelope walls are locally heated at points adjacent to at least some of the support members to produce small indentations forming inwardly projecting shoulders which are adapted to be located under and engaged by peripheral portions of the said support members when the lamp is disposed vertically, whereby to prevent the supports from sliding downward when the filament is heated, and thus keeping the filament in place.

Further features and advantages of my invention will appear from the following detailed description and from the drawing wherein:

Fig. 1 is..a vertical elevation, partly insection, of a lamp. comprisingrnylinvention; and.

Fig. 2 isa fragmentaryperspective view of a portion of the filament and an associated support member.

The particular lamp shown in Fig. lis-of the'type disclosed and claimed in Patent 2,864,205, Foote et al., and the specific filament-support member illustrated in 'Fig. 2 is of the type disclosed and claimed-in Patent 2,813,993, Fridrich, both patentsbeingassigned to the sameassignee as the present application. V

Referring to Fig. 1 of the drawing, the lamp comprises an elongated tubular envelope 1, preferably of quartz of small diameter, for example inch, and containing an atmosphere of inert gas, preferably argon, at a pressure preferably somewhatunder atmospheric at room tempera: ture, say about550 mm. of mercury. A helically coiled tungsten wire filament 2- extends axially of the envelope 1 and-is secured at'its ends to terminal members preferably consisting of molybdenum wire Shaving extremely thin (.0005 to .0010 inch) intermediate foliatedor ribbon portions. 4 sealed incompressed pinch sealportions 5 at the respective ends of the envelope. The filament under slight tension by virtue of having been stretched slightly during the sealing of-the lead wires- 3 into the pinch or press portions 5.

For supporting the filament 2 in spaced relation from the walls ofthe envelope, there are provided a plurality of transverse support members 6, preferably in the form of wafers or discs of tantalum sheet metal located at spaced intervals of about one inch and having a diameter slightly lessthan the interior diameter of the envelope 1. The discs 6 are preferably of the type disclosed and claimed in the aforesaid Fridrich Patent 2,8-13,9 93 and are securedly fixedto the filament, preferably by the method and apparatus disclosed and claimed in Patent 2,813,327, Fridrich. Each of the discs 6 is disposed transversely between two successive turns of the filament coil 2 and is pierced interiorly of the coil to form a central aperture with a short collar portion comprising tabs or tongues 7 curled about the adjacent turn of the filament coil to securely lock the disc to the filament. For purposes of assembly, the disc is provided with a radial slit 8 which is flared at 9 to facilitate insertion of the filament wire into the slit prior to formation of the tabs 7.

As thus far described, the filament 2 is subject to stretching and distortion when the lamp is operated in a vertical position. In accordance with the present invention, this is prevented by the provision of means to support the filament at intervals along its length so that it cannot stretch sufliciently to buckle. This is accomplished by the provision of inwardly projecting shoulders 10 located under some of the disc supports 6 and serving to keep the discs from sliding downward, thereby keeping the filament in place. Experience has shown that sufiicient support is aiforded by providing the shoulders 10 under every fifth disc 6 when said discs are spaced one inch apart. However, it will be understood that the spacing of the shoulders 10 may be varied for filament coils having different values of weight per unit of length.

The shoulders 10 are formed, after assembly of the lamp has been completed, by heating the quartz envelope 1 next to the disc supports 10 with a fine oxyhydrogen torch flame indicated at 11 whereby, under the subatmospheric pressure in the envelope, the wall thereof is drawn in to produce a small indentation forming a shoulder '10. Two such indentations at diametrically opposed points adjacent each disc 6 have been found to be effective, although a greater number may of course be employed when desired. It will also be understood that, when desired, the shoulders may be provided at both sides of the discs, as indicated by the shoulders 10' in Fig. 1, whereby to support the discs when the lamp is operated with either end uppermost.

By forming the indentations and shoulders 10 after the lamp has been otherwise completed, the said indentations do not in any way interfere with the threading of the filament 2 and its attached supports 6 and leads 3 into the envelope 1 before the seals 5 are formed.

- What I claim as new and desire to secure by Letters Patent of the United States is:

1.' An incandescent electric lamp device comprising a sealed elongated tubular. envelope of vitreous material, current supply terminals sealed in the respective ends of said envelope, a helically coiled wire filament extending longitudinally within said envelope and electrically connected at its ends to said terminals, means supporting said filament in spaced relation from the walls of said envelope comprising a plurality of transverse support members spaced along the length of said filament and fixedly secured thereto and peripherally engageable with the inner wall of said envelope, said envelope having indentations in portions of its walls contiguous to at least one side of at least some of said support members, said indentations forming inwardly projecting shoulders adapted to be located under and engaged by peripheral portions of said support members when the lamp device is vertically disposed whereby to support the coiled filament against sagging longitudinally during operation at incandescence.

2. An incandescent electric lamp device comprising a sealed elongated tubular envelope of vitreous material and adapted to be vertically disposed in normal use, current supply terminals sealed in the respective ends of said envelope, 9. helically coiled wire filament extending long itudinally within said envelope and electrically connected at its ends to said terminals, means supporting said filament in spaced relation from the walls of said envelope comprising a plurality of transverse support members spaced along the length of said filament and fixedly secured thereto and peripherally engageable with the inner wall of said envelope, said envelope having indentations in portions of its walls contiguous to and under at least some of said support members, said indentations forming inwardly projecting shoulders engaged by peripheral portions of said support members to support the coiled filament against sagging longitudinally downward during operation at incandescence.

3. An incandescent electric lamp device comprising a sealed elongated tubular envelope of vitreous material, current supply terminals sealed in the respective ends of said envelope, a helically coiled Wire filament extending longitudinally within said envelope and electrically connected at its ends to said terminals, means supporting said filament in spaced relation from the walls of said envelope comprising a plurality of transverse discs spaced along the length of said filament and fixedly secured thereto concentrically of the filament and peripherally engageable withthe inner wall of said envelope, said envelope having indentations in portions of its walls contiguous to at least one side of at least some of said discs, said indentations forming inwardly projecting shoulders adapted to be located under and engaged by peripheral portions of said discs when the lanip device is verti-' cally disposed whereby to support the coiled filament against sagging longitudinally during operation at incandescence.

References Cited in the file of this patent UNITED STATES PATENTS 821,470 Dempster May 22, 1906 1,306,912 Keyes June 17, 1919 1,963,008 Weeks June 12, 1934 2,219,111 Nicoll Oct. 22, 1940 2,813,993 Fridrich Nov. 19. 1957 

